56 A BOOK OF INSECTS 



injury. The spinous legs of dragon-flies form a kind of 

 basket for catching prey on the wing; they also enable 

 the insect to cling to a leaf or a grass blade, but they are 

 of little service for walking. Indeed, in most adult insects 

 which pass the greater part of their lives in flight, the legs 

 are relatively feeble ; while a few simplified insects have 

 no legs at all. 



Three pairs of thoracic or " true " legs, each terminat- 

 ing in a single claw, are present in most larvae — one pair 

 on each of the three segments immediately succeeding 

 the head ; but caterpillars also possess a varying number 

 of abdominal claspers or prolegs. Each proleg generally 

 ends in a circlet of minute hooks, by means of which a 

 firm hold is gained. The caterpillars of butterflies and 

 moths usually have ten prolegs — a pair on the seventh, 

 eighth, ninth, tenth, and thirteenth segments of the 

 body (the head being reckoned as the first segment), 

 but many " looper " caterpillars, of the family Geo?net7'idce, 

 have only two pairs — on the tenth and last segments 

 respectively. When walking, they first bring the hind 

 part of the body forward, so that the tenth segment 

 almost touches the fourth ; then, leaving the prolegs 

 fixed, they stretch out the body to its full length, and 

 take hold again with the three pairs of thoracic legs. 

 Thus their progress consists of a series of loops, whence 

 their popular name. The caterpillars of saw-flies have 

 seven or eight pairs of prolegs, while those of scorpion- 

 flies have eight pairs. Many other larvae have abdominal 

 organs which assist locomotion, but they are not so highly 

 specialised as the prolegs of caterpillars. 



